No crank No start

I drove my truck home 2 weeks ago. I turned it off, ran upstairs, changed
clothes, got back in truck to find it would not start.  The dash lights come on,
the radio and air conditioner came on and the headlights.  A friend
suggested the starter was out so I replaced it with a new starter and still, no
start. I changed the igniition switch, not the ignition lock, just the switch and
still, no start.  I changed the starter relay and the crank/run relay still, no
start.  Today, a mechanic came over and tried to jump the starter from the
battery and it turned over for the first time in 2 weeks, however no start. He
hooked a diagnostic tool up to it and it said no communication with ECU.
Does that mean for sure that the ECU is out?  I have read that if I buy
another ECU it has to be programmed. Also, for the first time, I see a lock on
top of a car that is showing up on my dash lights.